Critical criteria

What constitutes a good instructional product in my mind? To a degree, it depends on the subject being taught, of course. There are, however, come common criteria that I hope a book or video course would meet. 

First, the instructor has to be able to communicate and demonstrate his lessons in a coherent and understandable manner. Everything else hinges on this one. One of my greatest regrets is seeing promising material in terms of contents, being ruined by plain bad writing or incoherent and unintelligible mumbling. Now, don't get me wrong - I don't insist on Shakespearean penmanship and absolute grammatical or orthographic precision in a book, nor Harvard Law School rhetoric level on video; but what you read or watch needs to make enough sense that it doesn't leave you scratching your head and having no idea what you need to do with the material, how to approach it and why. 

That said, author's personal writing style or spoken accent and prosody don't mean much, as long as they are able to teach in a flowing and engaging fashion.  Naturally, some authors are more comfortable in one of these two formats, and that is perfectly fine. I like both, with some preference for books over videos. 

Second, the product should be presented systematically, following the progression that makes sense. Again, depending on the chosen topic and learner's prior level, there may be some flexibility here, but like any other story, if things are just thrown out randomly it only frustrates those trying to learn something from the material. That is why I ended up seriously disliking some of the "instructional" videos done by big name players back in the 1980's and 1990's - they were nothing but a bunch of loosely collected licks and lines that would fit well with the large majority of flashy Youtube demo clips of this age...with the notable difference of the former being rather costly back then. 

Third, there should be enough practice material for the students to develop solid understanding of the offered concepts and principles, and ideally with enough stimulating ideas for them to come up with their own examples and exercises around the same subject. 

Closely related to the previous one, the lessons ought to have balanced breadth/depth ratio. What does it mean? Essentially, if the product tries to squeeze too many topics in in a single package, it will inevitably lead to many of them, if not all, being just taken glance at, i.e. lacking any substantial understanding. We have all seen the products titled "Ultimate Complete Encyclopedia of Styles" with 500 unrelated two- or four-bar lines, yet with zero explanation about how those lines were built or what are acceptable variations in their music idioms. Unless you are going to use it for sight reading practice, such books are pretty much useless. It is better to have separate volumes on different topics, but treated with adequate commitment to detail and underlying principles. 

Finally, there is the matter of value for the money. This aspect, too, can be subjective as it is affected by one's previous musical background, experience and affinities. Nonetheless, there are quite a few instructional items out there, which have unacceptable amount of filler material. I understand that it may often be the demand of the publisher to have a certain amount of pages or minutes...still, for the same price, I much prefer to have a book with examples done in just a couple of keys, but with larger number of examples, than one with fewer examples transposed to every key. On video, I'd rather see and hear the author show/perform different variation or options of exercises then yet another rendition of their greatest hits, even if done live, just for the package at hand. Or, have a shorter package for a lower price.